The present invention relates to the measurement of industrial processes, and more particularly, to measurement and control systems and methods of measurement which rely on detecting variations in a beam of energy which is altered by transmittance, scattering, or fluorescence interactions with the process material being measured. An example is a measuring system which utilizes nuclear radiation as the energy source.
Many measurement sensors have a nonlinear response with respect to the process variable being measured. When such sensors are operated in a manner such that the sensor output represents an average of the variable to be measured over some area of the measured material, instrument errors due to nonlinear averaging may result if the process material is nonhomogeneous. Specific examples include the use of beta radiation for the measurement of basis weight in the paper making industry, or the use of gamma or x-radiation to measure the weight per area of fiberglass insulation batts being produced.
Typically, the weight per unit area of sheet material, or basis weight, is measured on-line during production of the sheet by scanning the measurement sensors back and forth across the width of the sheet as the material moves along the process line. In the case of a transmission beta gauge, a beam of beta particles is emitted from a radiation source into one side of the sheet material and the transmitted radiation is detected on the other side. The transmitted radiation varies approximately exponentially as a function of the thickness or weight per unit area of the sheet. The radiation beam is usually collimated so that it passes through some finite surface area of the measured material and the transmitted radiation represents an average basis weight for that portion of the sheet. If the material has a nonuniform distribution of mass within the measurement area, then nonlinear exponential averaging will occur which is an undesirable source of measurement error.